||Study on biological control of soil-born fungal pathogens using Trichoderma species isolated in Bangladesh
MD. MONIRUL ISLAM
74 , 2016-03-23 , 新潟大学
学位の種類: 博士（農学）. 報告番号: 甲第4197号. 学位記番号: 新大院博（農）甲第158号. 学位授与年月日: 平成28年3月23日
Trichoderma spp. can be used as potential biological control agents for a wide range of plant pathogens in agricultural systems because of their high reproductive capacity, ability to survive under harsh conditions, efficiency in the utilization of unfavorable nutrients, capacity to modify the rhizosphere, strong aggressiveness against phytopathogenic fungi, and efficiency in promoting plant growth and defense mechanisms. These properties have made Trichoderma a ubiquitous genus that is present at high population densities in all habitats. These direct and indirect Trichoderma mechanisms may act coordinately and their importance in the biocontrol process depends on the Trichoderma strain, the antagonized fungus, the crop plant and the environmental conditions, including nutrient availability, pH, and temperature. This study was intended to corroborate the positive relationships of molecular and morphological characteristics with the antagonistic ability, as well as the physiological and biochemical features of Trichoderma species. Nineteen Trichoderma isolates, collected from different locations in Bangladesh, were characterized using phenotypic, biochemical and molecular means. Additionally, their antifungal actions were assessed in vitro. The isolates were divided into three groups: Trichoderma asperellum, Trichoderma virens and Trichoderma harzianum. Dual culture and culture filtrate assays against 6 phytopathogens revealed that 9 of the 19 isolates showed significant antifungal activities. The isolate T. harzianum TR05 showed the highest inhibition against Fusarium oxysporum, Rhizoctonia solani, Fusarium circinatum and Phomopsis vexans, followed by T. asperellum TR08 and T. virens TR06. TR08 had the highest inhibition against Sclerotium rolfsii and Pythium aphanidermatum, followed by TR05 and TR06. These findings were in agreement with the activities of their extracellular hydrolytic enzymes, including chitinase, β-1,3-glucanase and proteinase. In a pot experiment under greenhouse conditions, tomato seeds inoculated with TR05 (seed treatment) showed the lowest disease incidence and the highest germination. They also gave superior results in the following plant growth factors: root length, shoot length, fresh weight, dry weight and seedling vigor. In soil treatments, TR08 showed the lowest disease incidence and had superior plant growth factor values. Our results suggest that isolates TR05 and TR08 have the potential to be effective biocontrol agents against phytopathogenic fungi.